The amount of information processed by various types of electronic devices has been increasing in recent years, and this has been accompanied by rapid advances in packaging technology, e.g., greater integration for the mounted semiconductor devices, higher interconnect densities, and multilayering. The insulating materials in, for example, the printed wiring boards used in various electronic devices, must have a low dielectric constant and a low dissipation factor in order to increase the signal transmission velocity and lower the losses during signal transmission and must have a high glass-transition temperature (Tg) to support the more extensive multilayering brought about by the addition of wiring.
Polyphenylene ether (PPE) has excellent dielectric properties, e.g., dielectric constant and dissipation factor, even in the high-frequency band (high-frequency region) from the MHz band to the GHz band, and because of this it is advantageously used for the insulating materials in, for example, printed wiring boards, in electronic devices that use the high-frequency band. However, high molecular weight PPE generally has a high melting point and as a consequence tends to have a high viscosity and a low fluidity. Moldability problems have appeared—i.e., molding defects, for example, the appearance of voids during multilayer molding, have been produced during fabrication and the preparation of highly reliable printed wiring boards has been problematic—when such a PPE has been used to form a prepreg for the fabrication of, e.g., a multilayer printed wiring board, and a printed wiring board has then been fabricated using the thusly formed prepreg. In order to solve such problems, for example, an art is known in which molecular scission is induced and the molecular weight of the PPE is reduced by carrying out a redistribution reaction on the high molecular weight PPE in a solvent in the presence of a phenol and a radical initiator. However, there have been problems with reducing the molecular weight of PPE in that the cure becomes inadequate and, inter alia, the heat resistance of the cured product is reduced.
The resin compositions described in the Patent Documents 1 to 4 given below are examples of resin compositions that contain a resin in which the main component is an aromatic polyether structure such as, for example, PPE.
The curable polyphenylene ether composition described in Patent Document 1 contains a curable unsaturated monomer and a polyphenylene ether that contains a hydroxyl group that has been capped by a compound containing ethylenic unsaturation.
The flame-retardant composition described in Patent Document 2 comprises a polyphenylene ether and a phosphazene compound.
The curable composition disclosed in Patent Document 3 comprises an epoxy resin, a bifunctional polyarylene ether, and a curing catalyst in an amount effective for curing the epoxy resin, and yields a cured product with a prescribed impact strength value.
The resin compound disclosed in Patent Document 4 comprises a polyarylene ether copolymer having prescribed properties, an epoxy resin, a cure accelerator, and a phosphorus-containing compound having prescribed properties.
Patent Document 1: U.S. Pat. No. 6,352,782
Patent Document 2: Japanese Patent No. 3886053
Patent Document 3: WO 2008/033611
Patent Document 4: Japanese Patent Application Laid-open No. 2011-46816
However, the resin described in Patent Document 1 in which the main component is an aromatic polyether structure is a monofunctional PPE having an intrinsic viscosity of 0.15 dL/g. When a resin composition provided by combining such a PPE with an epoxy resin was made into a resin varnish, a high viscosity was produced and a trend of a rising viscosity with elapsed time (i.e., a declining fluidity) also appeared. In particular, this trend became quite pronounced when the PPE proportion was raised. Moldability problems appeared—i.e., molding defects, for example, the appearance of voids during multilayer molding, were produced during fabrication and the preparation of a highly reliable printed wiring board was problematic—when such a resin composition was used to form a prepreg and a printed wiring board was then fabricated using the thusly formed prepreg. Moreover, the composition described in Patent Document 1 used a brominated flame retardant as its flame retardant and was thus not an environmentally friendly halogen-free material.
A problem with the resin composition described in Patent Document 2 was that it lacked the solder heat resistance required for application with electronic components. Specifically, the blending of a monofunctional PPE with a difunctional epoxy resin is described in the examples. However, this resin composition, although it could secure flame retardancy while being halogen-free, had a low Tg and an inadequate solder heat resistance. It is hypothesized from this that the flame retardancy was raised due to the incorporation of the phosphazene compound, but that this phosphazene compound acted as a plasticizer and three-dimensional crosslinking was required. In addition, the PPE with its excellent dielectric properties was incorporated at not more than 50 mass % and thus the dielectric properties were also inadequate.
In addition, Patent Document 3 states that a flame retardant may be incorporated in the resin composition comprising a polyarylene ether and an epoxy resin. However, when a flame retardant was incorporated, a trend of a declining heat resistance by the cured product was present and in some cases the heat resistance of the cured product and the dielectric properties were not adequate.
In comparison to the resin compositions in Patent Documents 1 to 3, the resin composition described in Patent Document 4 is considered to be a resin composition that has a better heat resistance by the cured product, better dielectric properties, and a higher flame retardancy and that provides a lower viscosity (i.e., has better handling characteristics) when made into a varnish. However, even higher glass-transition temperatures (Tg) have come to be required in recent years due to the more extensive multilayering brought about by the addition of wiring, and thus at the present time a resin composition is required that has, in addition to the previously described properties, a higher glass-transition temperature (Tg).